I am using the OpenJMS with derby DB. I ran some performance tests and at the end of it I found DB folder size in 7.1 GB. The opemJMS clears the tables after the messages are delivered. I verified that the tables don't have much data using in. Why then there are large sized .dat files in the database folder?  Is there any DB configuration  parameter which can be used to limit this size and hence the derby does the clean up before the next insertion?